獲取錯誤：EXC_BAD_INSTRUCTION（code = EXC_I386_INVOP，subcode = 0x0），爲什麼？

Question

我的代碼如下：

let mvc = MainViewController() 
    let average = mvc.defaults.array(forKey: "grades") as! [Int] 
    let averagePoints = mvc.defaults.integer(forKey: "averagePoints") 
    gradePoints = averagePoints/average.count 

在最後一行，我得到一個EXC_BAD_INSTRUCTION（代碼= EXC_I386_INVOP，子碼=爲0x0）的錯誤。這是什麼意思，爲什麼我能得到它？

謝謝你的幫助！

Answer 1

嘗試這種情況：

if let average = mvc.defaults.array(forKey: "grades") as? [Int], 
    let averagePoints = mvc.defaults.integer(forKey: "averagePoints") { 
    gradePoints = averagePoints/average.count 
} 

好像grades陣列或/和averagePoints是/是零。